Multilayered piezoelectric/electrostrictive device

ABSTRACT

A multilayered piezoelectric/electrostrictive device includes a substrate  1 , a plurality of piezoelectric/electrostrictive portions  2  and  3 , and a plurality of electrodes  4, 5 , and  6 ; the piezoelectric/electrostrictive portions  2  and  3  and the electrodes  4, 5 , and  6  being alternately layered on the substrate  1 , and the piezoelectric/electrostrictive portion  12  positioned in the lowermost layer being anchored to the substrate  1  directly or through the electrode  4 . The ratio α given by the average particle size (A) (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion to the thickness (B) (μm) of the piezoelectric/electrostrictive portion satisfies the relationship expressed by “0.02≦α≦0.6” in each of the piezoelectric/electrostrictive portions  2  and  3.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a multilayered piezoelectric/electrostrictive device. More particularly, the present invention relates to a multilayered piezoelectric/electrostrictive device which includes a piezoelectric/electrostrictive portion having extremely excellent piezoelectric/electrostrictive characteristics. This device is excellent in vibration transfer characteristics between the substrate and the piezoelectric/electrostrictive portion, shows small variation in piezoelectric/electrostrictive characteristics even within the portions of a single piezoelectric/electrostrictive portion, and exhibits excellent durability.

[0003] 2. Description of Related Art

[0004] A piezoelectric/electrostrictive device is known as a device which can control micro-displacement in the order of submicrons. A piezoelectric/electrostrictive device in which a piezoelectric/electrostrictive portion formed of a piezoelectric/electrostrictive ceramic composition and an electrode portion to which voltage is applied are layered on a ceramic substrate is generally used. In recent years, a multilayered piezoelectric/electrostrictive device in which a number of piezoelectric/electrostrictive portions and electrodes are alternately layered on the substrate is also used, since the output can be increased at a low applied voltage. The multilayered piezoelectric/electrostrictive device is suitable for controlling micro-displacement and has excellent characteristics such as high electrical/mechanical conversion efficiency, high-speed response, high durability, and small power consumption. Thus, the multilayered piezoelectric/electrostrictive device is used in various applications such as a piezoelectric pressure sensor, a probe moving mechanism for a scanning tunneling microscope, a linear guide mechanism for an ultra-precision machining device, a hydraulic pressure control servo valve, a head for a VTR device, a pixel used for forming a flat panel image display device, or a head for an ink-jet printer.

[0005] Various studies have been made on the piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion. For example, a Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃—PbZrO₃ three-component solid solution composition or a piezoelectric/electrostrictive ceramic composition obtained by replacing a part of Pb in this composition with Sr or La is disclosed (see JP-A-44-17103 and JP-A-45-8145, for example). It was expected that one may obtain a piezoelectric/electrostrictive device having excellent piezoelectric/electrostrictive characteristics (piezoelectric d constant, for example) by using this composition to produce a piezoelectric/electrostrictive portion itself, which is the most important element that determines the piezoelectric/electrostrictive characteristics of the piezoelectric/electrostrictive device.

[0006] However, in case of the conventional piezoelectric/electrostrictive device, the piezoelectric/electrostrictive device is manufactured by performing a heat treatment after forming a piezoelectric/electrostrictive ceramic formed of the piezoelectric/electrostrictive ceramic composition on the substrate. Thus, the contraction and the densification of the piezoelectric/electrostrictive ceramic composition during the heat treatment are hindered because the substrate hardly contracts. Accordingly, the density of the piezoelectric/electrostrictive portion is decreased. As a result, one should often face to a problem such as the decrease in the bending displacement or the occurrence of the dielectric breakdown in the area in which the density is low when voltage is applied to piezoelectric/electrostrictive portion. This problem becomes striking in the multilayered piezoelectric/electrostrictive device, and improvement is strongly demanded.

[0007] In view of the above-described situation, there is a proposal in JP-A-11-29357 that the densification of a piezoelectric/electrostrictive portion is attained by mounting a piezoelectric/electrostrictive portion obtained by heating a piezoelectric/electrostrictive ceramic to the substrate; said piezoelectric/electrostrictive ceramic having been formed of a piezoelectric/electrostrictive ceramic composition by heating the piezoelectric/electrostrictive ceramic in advance. However, in the case of this type of the piezoelectric/electrostrictive device, it is necessary to use an inorganic or organic adhesive when the piezoelectric/electrostrictive portion is mounted to the substrate. The adhesive used hinders vibration transfer between the substrate and the piezoelectric/electrostrictive portion, or the adhesive component deteriorates the characteristics of the piezoelectric/electrostrictive portion or the substrate.

[0008] In the case where variation in piezoelectric/electrostrictive characteristics occurs between the piezoelectric/electrostrictive portions or between portions (center and end, for example) within a single piezoelectric/electrostrictive portion, if the piezoelectric/electrostrictive device including such a piezoelectric/electrostrictive portion is provided in an electronic instrument such as a transmitter or a sensor, excellent transmission or accurate sensing can be hardly attained. Moreover, a piezoelectric/electrostrictive device having variation in piezoelectric/electrostrictive characteristics between portions within a single piezoelectric/electrostrictive portion may pose a problem relating to durability due to stress concentration caused by variation in bending displacement.

[0009] In order to solve the above-described problems, a piezoelectric device including a piezoelectric portion formed of a piezoelectric ceramic composition containing a specific Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition, in which a part of the Mg is replaced with Ni, as an essential component is disclosed (see JP-A-2002-388315, for example). However, the piezoelectric device disclosed in JP-A-2002-388315 does not fully eliminate the variation in piezoelectric/electrostrictive characteristics between the piezoelectric/electrostrictive portions or between portions (center and end, for example) within a single piezoelectric/electrostrictive portion. Moreover, further improvement of durability is strongly demanded.

SUMMARY OF THE INVENTION

[0010] The present invention has been made in view of the above-described problems in the conventional art. Therefore, the present invention is to provide a multilayered piezoelectric/electrostrictive device which includes a piezoelectric/electrostrictive portion having extremely excellent piezoelectric/electrostrictive characteristics; said multilayered piezoelectric/electrostrictive device being excellent in vibration transfer characteristics between the substrate and the piezoelectric/electrostrictive portion, showing small variation in piezoelectric/electrostrictive characteristics between piezoelectric/electrostrictive portions or the portions within a single piezoelectric/electrostrictive portion, and exhibiting excellent durability.

[0011] According to the present invention, there is provided a multilayered piezoelectric/electrostrictive device comprising a ceramic substrate, a plurality of piezoelectric/electrostrictive portions including a piezoelectric/electrostrictive ceramic formed of a piezoelectric/electrostrictive ceramic composition, and a plurality of electrodes electrically connected with the piezoelectric/electrostrictive portion, the piezoelectric/electrostrictive portions and the electrodes being alternately layered on the substrate, and a lowermost piezoelectric/electrostrictive portion of the piezoelectric/electrostrictive portions positioned in a lowermost layer adhering to the substrate directly or through a lowermost electrode of the electrodes positioned in a lowermost layer, wherein a ratio (α=A/B) of an average particle size (A) (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion to a thickness (B) (μm) of the piezoelectric/electrostrictive portion satisfies a relationship expressed by “0.02≦α≦0.6” in each of the piezoelectric/electrostrictive portions.

[0012] In the present invention, it is preferable that the maximum particle size (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion be smaller than the thickness (μm) of the piezoelectric/electrostrictive portion in each of the piezoelectric/electrostrictive portions.

[0013] In the present invention, it is preferable that the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion be 0.06-0.84 mass % (NiO conversion), and the Ni content in terms of NiO in the piezoelectric/electrostrictive ceramic composition used for forming each of the piezoelectric/electrostrictive portions in layers except the lowermost piezoelectric/electrostrictive portion be equal to or greater than the Ni content in terms of NiO in the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion.

[0014] In the present invention, it is preferable that the thickness of the piezoelectric/electrostrictive portion be 1-50 μm. In the present invention, it is also preferable that the piezoelectric/electrostrictive ceramic composition comprise a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition shown by the following formula (1) as an essential component:

Pb_(x){(Mg_(1−y)Ni_(y))_((1/3)xa)Nb_(2/3)}_(b)Ti_(c)Zr_(d)O₃  (1)

[0015] wherein 0.95≦x≦1.05, 0.05≦y≦0.50, 0.90≦a≦1.10, and each of b, c, and d is a decimal within the range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (b+c+d)=1.000.

[0016] In the present invention, it is preferable that the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion comprise a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition shown by the following formula (2) as an essential component, and the piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion positioned in a layer above the lowermost piezoelectric/electrostrictive portion comprise a PbMg_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO three-component solid solution composition shown by the following formula (3) as an essential component and include NiO:

Pb_(x){(Mg_(1−y)Ni_(y))_((1/3)xa)Nb_(2/3)}_(b)Ti_(c)Zr_(d)O₃  (2)

[0017] wherein 0.95≦x≦1.05, 0.05≦y≦0.50, 0.90≦a≦1.10, and each of b, c, and d is a decimal within the range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d)=(b, c, d)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (b+c+d) is 1.000; and

Pb_(x)(Mg_(y/3)Nb_(2/3))_(a)Ti_(b)Zr_(c)O₃  (3)

[0018] wherein 0.95≦x≦1.05, 0.95≦y≦1.050, and each of b, c, and d is a decimal within the range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d)=(a, b, c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (a+b+c) is 1.000.

BRIEF DESCRIPTION OF THE DRAWING

[0019]FIG. 1 is a cross-sectional view schematically showing an embodiment of a multilayered piezoelectric/electrostrictive device of the present invention.

[0020]FIG. 2 is a cross-sectional view schematically showing another embodiment of a multilayered piezoelectric/electrostrictive device of the present invention.

[0021]FIG. 3 is a cross-sectional view schematically showing another embodiment of a multilayered piezoelectric/electrostrictive device of the present invention.

[0022] FIGS. 4(a) and 4(b) are views schematically showing another embodiment of a multilayered piezoelectric/electrostrictive device of the present invention, in which FIG. 4(a) is a top view and FIG. 4(b) is a cross-sectional view.

[0023]FIG. 5 is a view schematically showing still another embodiment of a multilayered piezoelectric/electrostrictive device of the present invention, in which FIG. 5(a) is a top view, FIG. 5(b) is a cross-sectional view along the line A-A′ shown in FIG. 5(a), and FIG. 5(c) is a cross-sectional view along the line B-B′ shown in FIG. 5(a).

[0024]FIG. 6 is a cross-sectional view showing a more detailed example of the embodiment shown in FIG. 2.

[0025]FIG. 7 is a cross-sectional view showing another detailed example of the embodiment shown in FIG. 2.

[0026]FIG. 8 is a cross-sectional view showing another detailed example of the embodiment shown in FIG. 2.

[0027]FIG. 9 is a cross-sectional view showing another detailed example of the embodiment shown in FIG. 2.

[0028]FIG. 10 is a cross-sectional view showing another detailed example of the embodiment shown in FIG. 2.

[0029]FIG. 11 is a cross-sectional view showing still another detailed example of the embodiment shown in FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0030] The embodiments of the present invention are described below. However, the present invention is not limited to the following embodiments. Various modifications and improvements of the design can be made within the scope of the present invention based on knowledge of a person skilled in the art. A multilayered piezoelectric/electrostrictive device including two layers of piezoelectric/electrostrictive portions is mainly described below as an example. However, a multilayered piezoelectric/electrostrictive device including three or more layers of piezoelectric/electrostrictive portions is also included within the scope of the present invention.

[0031] As shown in FIG. 1, a multilayered piezoelectric/electrostrictive device which is an embodiment of the present invention includes, on a ceramic substrate 1, piezoelectric/electrostrictive portions 2 (first piezoelectric/electrostrictive portion 12) and 3 (second piezoelectric/electrostrictive portion 13) including a piezoelectric/electrostrictive ceramic formed of a piezoelectric/electrostrictive ceramic composition, and electrodes 4 and 5 electrically connected with the piezoelectric/electrostrictive portions 2 and 3. FIG. 1 shows a state in which the piezoelectric/electrostrictive portions 2 and 3 and the electrodes 4 and 5 are alternately layered on the substrate 1, and the lowermost piezoelectric/electrostrictive portion (first piezoelectric/electrostrictive portion 12) of the piezoelectric/electrostrictive portions 2 and 3 positioned in the lowermost layer adheres to the substrate 1 through the lowermost electrode (electrode 4) of the electrodes 4 and 5 positioned in the lowermost layer.

[0032] In the present invention, the first piezoelectric/electrostrictive portion which is the lowermost piezoelectric/electrostrictive portion may directly adhere to the substrate without the electrode interposed therebetween. Each anchoring state can prevent a decrease in vibration transfer characteristics between the substrate and the piezoelectric/electrostrictive portion caused by the presence of an adhesive or the like, and prevent deterioration of the characteristics of the piezoelectric/electrostrictive portion or the substrate caused by the effect of an adhesive component or the like. The term “anchoring” used herein means a state in which the piezoelectric/electrostrictive portion and the substrate are closely integrated without using an organic or inorganic adhesive due to the solid phase reaction between the piezoelectric/electrostrictive portion and the substrate or the electrode.

[0033] In the multilayered piezoelectric/electrostrictive device of the present embodiment, provided that the thickness of the piezoelectric/electrostrictive portions 2 and 3 is denoted by B (μm) and the average particle size of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portions 2 and 3 is denoted by A (μm), the ratio a satisfies the relationship expressed by “0.02≦α≦0.6” in each of the piezoelectric/electrostrictive portions 2 and 3 wherein the ratio a is a ratio between said A and said B. In the present specification, the term “ratio α” herein after means a ratio between an average particle size A (μm) of a piezoelectric/electrostrictive ceramic used for forming a piezoelectric/electrostrictive portion and a thickness B (μm) of the piezoelectric/electrostrictive portion. In other words, the particle size of the piezoelectric/electrostrictive ceramic used for a specified single piezoelectric/electrostrictive portion is preferably within a predetermined range in the relationship with the thickness of said specified single piezoelectric/electrostrictive portion. Therefore, since variation in piezoelectric/electrostrictive characteristics in each of the piezoelectric/electrostrictive portions 2 and 3 is small, the multilayered piezoelectric/electrostrictive device of the present embodiment is suitable as a piezoelectric/electrostrictive device to be disposed in an electronic instrument such as a transmitter or a sensor for which excellent transmission or accurate sensing is required. Moreover, since variation in piezoelectric/electrostrictive characteristics in each of the piezoelectric/electrostrictive portions 2 and 3 is small, stress concentration caused by variation in bending displacement can be prevented. Therefore, since the multilayered piezoelectric/electrostrictive device of the present embodiment rarely poses a problem such as a significant decrease in piezoelectric/electrostrictive characteristics or stress fracture during use for a long time, the multilayered piezoelectric/electrostrictive device of the present embodiment exhibits excellent durability.

[0034] If the ratio a exceeds 0.6, variation in piezoelectric/electrostrictive characteristics in the device is increased. If the ratio α is below 0.02, the piezoelectric/electrostrictive characteristics gradually decrease, whereby it may be difficult to secure sufficient displacement. In the multilayered piezoelectric/electrostrictive device of the present invention, the ratio α preferably satisfies the relationship expressed by “0.2≦α≦0.4” in each piezoelectric/electrostrictive portion from the viewpoint of further reducing variation in piezoelectric/electrostrictive characteristics in each piezoelectric/electrostrictive portion and providing further excellent durability.

[0035] In the multilayered piezoelectric/electrostrictive device of the present invention, the maximum particle size (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portions 2 and 3 is preferably smaller than the thickness (μm) of the piezoelectric/electrostrictive portion in each of the piezoelectric/electrostrictive portions 2 and 3. If the maximum particle size (μm) is greater than the thickness (μm) of the piezoelectric/electrostrictive portion, a piezoelectric/electrostrictive ceramic having a considerably large particle size may be included as any one of the piezoelectric/electrostrictive portions, even if the thickness (B) of the piezoelectric/electrostrictive portion and the average particle size (A) of the piezoelectric/electrostrictive ceramic can satisfy the relationship shown by the ratio a specified above. This is because the presence of particles having such a large size would bring variation in piezoelectric/electrostrictive characteristics of the piezoelectric/electrostrictive portion.

[0036] In the multilayered piezoelectric/electrostrictive device of the present invention, it is preferable that the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion (first piezoelectric/electrostrictive portion 12) be 0.06-0.84 mass %, and the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming each of the piezoelectric/electrostrictive portions (second piezoelectric/electrostrictive portion 13 in FIG. 1) positioned in the layer above the first piezoelectric/electrostrictive portion 12 be equal to or greater than the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming the first piezoelectric/electrostrictive portion 12. If the piezoelectric/electrostrictive ceramic composition contains Ni in the above predetermined content, since the formation of a heterophase is prevented in the first piezoelectric/electrostrictive portion 12 and the proportion of the perovskite phase which contributes to bending displacement is increased, the piezoelectric/electrostrictive characteristics can be improved by the characteristics of the composition. Moreover, since the piezoelectric/electrostrictive portion (second piezoelectric/electrostrictive portion 13) having a higher Ni content and positioned in the layer above the first piezoelectric/electrostrictive portion 12 is restricted by the substrate 1 to only a small extent with respect to sintering shrinkage, the effect of the addition of Ni becomes significant. Therefore, the piezoelectric/electrostrictive portion (second piezoelectric/electrostrictive portion 13) positioned in the layer above the first piezoelectric/electrostrictive portion 12 is highly densified by a heat treatment in the manufacturing step, and the adjacent first piezoelectric/electrostrictive portion 12 is also densified by the effect of the second piezoelectric/electrostrictive portion 13. Therefore, the multilayered piezoelectric/electrostrictive device of the present embodiment has higher piezoelectric/electrostrictive characteristics in combination with the characteristics of the piezoelectric/electrostrictive ceramic composition.

[0037] In the multilayered piezoelectric/electrostrictive device of the present embodiment, the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming the first piezoelectric/electrostrictive portion 12 is still more preferably 0.15-0.8 mass %, and particularly preferably 0.18-0.25 mass % from the viewpoint of further densifying the first piezoelectric/electrostrictive portion 12 in addition to the prevention of forming a heterophase in the piezoelectric/electrostrictive portion.

[0038] In the multilayered piezoelectric/electrostrictive device of the present embodiment, the Ni content ratio (first/second) shown by the ratio of the Ni content (mass % (NiO conversion)) in the piezoelectric/electrostrictive ceramic composition used for forming the first piezoelectric/electrostrictive portion 12 to the Ni content in mass % in the piezoelectric/electrostrictive ceramic composition used for forming the second piezoelectric/electrostrictive portion 13 is preferably 0.2-1.0, still more preferably 0.3-1.0, and particularly preferably 0.5-1.0. If the Ni content ratio (first/second) is below 0.2, the particle size of the piezoelectric/electrostrictive ceramic used for forming the first piezoelectric/electrostrictive portion and the second piezoelectric/electrostrictive portion is increased, whereby the entire piezoelectric/electrostrictive characteristics are decreased. That is, variation in bending displacement in the piezoelectric/electrostrictive device is increased. If the Ni content ratio exceeds 1.0, the particle size of the piezoelectric/electrostrictive ceramic used for forming the first piezoelectric/electrostrictive portion and the second piezoelectric/electrostrictive portion is decreased, whereby the entire piezoelectric/electrostrictive characteristics are decreased; that is, the bending displacement of the piezoelectric/electrostrictive device is decreased.

[0039] In the multilayered piezoelectric/electrostrictive device of the present invention, the thickness of one piezoelectric/electrostrictive portion (first piezoelectric/electrostrictive portion 12 or second piezoelectric/electrostrictive portion 13 in FIG. 1) is preferably 1-50 μm, still more preferably 2-40 μm, and particularly preferably 3-30 μm. If the thickness of the piezoelectric/electrostrictive portion is below 1 μm, densification of the piezoelectric/electrostrictive portions tends to become insufficient even if the piezoelectric/electrostrictive portions is made of the piezoelectric/electrostrictive ceramic by using the piezoelectric/electrostrictive ceramic composition containing Ni in the above predetermined content. If the thickness of the piezoelectric/electrostrictive portion exceeds 50 μm, since it is necessary to increase the thickness of the substrate in order to prevent breakage of the substrate, it is difficult to deal with a reduction in size of the piezoelectric/electrostrictive device.

[0040] The piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion of the multilayered piezoelectric/electrostrictive device of the present invention preferably comprises a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition shown by the following formula (1) as an essential component. Since this three-component solid solution composition is prepared by replacing a part of Mg in a Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃—PbZrO₃ three-component solid solution composition with Ni, formation of a heterophase in the piezoelectric/electrostrictive portion is prevented and the proportion of the perovskite phase which contributes to bending displacement is increased, whereby the piezoelectric/electrostrictive characteristics are improved by the characteristics of the composition:

Pb_(x){(Mg_(1−y)Ni_(y))_((1/3)xa)Nb_(2/3)}_(b)Ti_(c)Zr_(d)O₃  (1)

[0041] wehrein 0.95≦x≦1.05, 0.05≦y≦0.50, 0.90≦a≦1.10, and each of b, c, and d is a decimal within the range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d) =(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (b+c+d) =1.000.

[0042] The piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion of the multilayered piezoelectric/electrostrictive device of the present invention preferably comprises a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition shown by the following formula (2) as an essential component, and the piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion positioned in the layer above the lowermost piezoelectric/electrostrictive portion preferably comprises a PbMg_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO three-component solid solution composition shown by the following formula (3) as an essential component and includes NiO:

Pb_(x){(Mg_(1−y)Ni_(y))_((1/3)xa)Nb_(2/3)}_(b)Ti_(c)Zr_(d)O₃  (2)

[0043] wherein 0.95≦x≦1.05, 0.05≦y≦0.50, 0.90≦a≦1.10, and each of b, c, and d is a decimal within the range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d) =(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (b+c+d) is 1.000.

Pb_(x)(Mg_(y/3)Nb_(2/3))_(a)Ti_(b)Zr_(c)O₃  (3)

[0044] wherein 0.95≦x≦1.05, 0.95≦y≦1.050, and each of b, c, and d is a decimal within the range enclosed by coordinates in which b, c, and d are axes of coordinates, (a, b, c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (a+b+c) is 1.000.

[0045] Specifically, formation of a heterophase in the piezoelectric/electrostrictive portion is prevented and the proportion of the perovskite phase which contributes to bending displacement is increased, whereby the piezoelectric/electrostrictive characteristics are improved by the characteristics of the composition. Moreover, since a reduction of Pb content from the perovskite structure is prevented in the piezoelectric/electrostrictive portion positioned in the layer above the lowermost piezoelectric/electrostrictive portion, the bending displacement of the piezoelectric/electrostrictive portion positioned in the upper layer is extremely increased, whereby the piezoelectric/electrostrictive characteristics are improved in the entire multilayered piezoelectric/electrostrictive device.

[0046] The substrate used for forming the multilayered piezoelectric/electrostrictive device of the present invention is formed of a ceramic. There are no specific limitations to the type of the ceramic. The substrate is preferably formed of a ceramic which includes at least one material selected from the group consisting of stabilized zirconium oxide, aluminum oxide, magnesium oxide, mullite, aluminum nitride, silicon nitride, and glass from the viewpoint of heat resistance, chemical stability, and insulating properties. The substrate is still more preferably formed of stabilized zirconium oxide, since the stabilized zirconium oxide has high mechanical strength and excellent toughness. The “stabilized zirconium oxide” used herein refers to zirconium oxide in which crystal phase transition is controlled by adding a stabilizer, and includes partially stabilized zirconium oxide in addition to the stabilized zirconium oxide.

[0047] As the stabilized zirconium oxide, stabilized zirconium oxide containing a stabilizer such as calcium oxide, magnesium oxide, yttrium oxide, scandium oxide, ytterbium oxide, cerium oxide, or an oxide of a rare earth metal in an amount of 1-30 mol % can be given. Of these, stabilized zirconium oxide containing yttrium oxide as the stabilizer is preferable, since the mechanical strength of the vibration portion is particularly increased. In this case, yttrium oxide is added in an amount of preferably 1.5-6 mol %, and still more preferably 2-4 mol %. It is preferable to use stabilized zirconium oxide further containing aluminum oxide in an amount of 0.1-5 mol %. The crystal phase of the stabilized zirconium oxide may be a mixed phase of a cubic phase and a monoclinic phase, a mixed phase of a tetragonal phase and a monoclinic phase, a mixed phase of a cubic phase, a tetragonal phase, and a monoclinic phase, or the like. The main crystal phase of the stabilized zirconium oxide is preferably a tetragonal phase or a mixed phase of a tetragonal phase and a cubic phase from the viewpoint of strength, toughness, and durability.

[0048] The thickness of the substrate is preferably 1 μm to 1 mm, still more preferably 1.5-500 μm, and particularly preferably 2-200 μm. If the thickness of the substrate is less than 1 μm, mechanical strength of the multilayered piezoelectric/electrostrictive device may be decreased. If the thickness of the substrate is greater than 1 mm, rigidity of the substrate against shrinkage stress of the piezoelectric/electrostrictive portion is increased when applying voltage, whereby bending displacement of the multilayered piezoelectric/electrostrictive device may be decreased.

[0049] As shown in FIG. 2, the substrate 1 may be formed in such a shape that the substrate 1 includes a thin portion 1 c which includes at least one anchoring surface 1 a to which the piezoelectric/electrostrictive portion 2 or the electrode 4 is anchored (FIG. 2 shows an example in which the electrode 4 is anchored to the substrate 1) and has the above predetermined thickness (thickness of the substrate), and a thick portion 1 b which is continuous with the thin portion 1 c and has a thickness greater than the thickness of the thin portion 1 c. The bending displacement and mechanical strength of the multilayered piezoelectric/electrostrictive device can be increased by forming the substrate 1 in such a shape. As shown in FIG. 3, a plurality of structural units may be formed on a common substrate 20, and the common substrate 20 may be used in common by a plurality of piezoelectric/electrostrictive devices 10.

[0050] In the embodiment of the multilayered piezoelectric/electrostrictive device of the present invention shown in FIGS. 5(a) to 5(c), the substrate 1 is formed in such a shape that the substrate 1 includes the sheet-shaped thin portion 1 c which includes at least one anchoring surface 1 a to which the piezoelectric/electrostrictive portion 2 (or electrode 4) is anchored and has the above predetermined thickness (thickness of the substrate), and a support portion 25 which is continuous with one end of the thin portion 1 c, and the electrodes 4, 5, and 6 and the piezoelectric/electrostrictive portions (first piezoelectric/electrostrictive portion 12 and second piezoelectric/electrostrictive portion 13) are alternately layered on the anchoring surface 1 a. In this case, the other end of the thin portion 1 c becomes an actuator portion 30 which is displaced in a predetermined direction (vertical direction in FIG. 5(b)) based on the bending displacement of the piezoelectric/electrostrictive portions (first piezoelectric/electrostrictive portion 12 and second piezoelectric/electrostrictive portion 13). Since the multilayered piezoelectric/electrostrictive device of the present embodiment exhibits accurate frequency characteristics due to extremely small variation in piezoelectric/electrostrictive characteristics between each portion of the piezoelectric/electrostrictive portion, accurate sensing can be performed by the actuator portion 30. Therefore, in the case where the multilayered piezoelectric/electrostrictive device of the present embodiment is provided in an electronic instrument such as a transmitter or a sensor, excellent transmission or accurate sensing can be easily achieved.

[0051] There are no specific limitations to the surface shape of the substrate in the present invention (shape of the surface to which the electrode 4 adheres in FIG. 1). For example, the surface shape of the substrate may be a rectangle, square, triangle, ellipse, circle, rounded square, rounded rectangle, or complex shape of these. There are no specific limitations to the shape of the substrate. The substrate may have a capsule shape with an appropriate internal space.

[0052] The thin portion of the substrate preferably has a shape in which the center is bent in the direction opposite to the surface having the piezoelectric/electrostrictive portions 2 and 3 as shown in FIG. 7, or a “W” shape in which the cross-sectional shape in the direction of the thickness has three inflection points as shown in FIG. 8. The bending shape shown in FIG. 7 may be formed by utilizing shrinkage of the piezoelectric/electrostrictive portions 2 and 3 in a heat treatment step, and the “W” shape shown in FIG. 8 may be formed by adjusting the sintering shrinkage start timing or the amount of sintering shrinkage of the piezoelectric/electrostrictive portion 2 and the piezoelectric/electrostrictive portion 3, or by adjusting the shape of the thin portion 1 c.

[0053] In the present invention, the electrode is electrically connected with the piezoelectric/electrostrictive portion, and is disposed between the piezoelectric/electrostrictive portions. If the electrode is disposed in this manner, in the case where the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion positioned in the layer above the lowermost piezoelectric/electrostrictive portion is equal to or greater than the Ni content in the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion, the electrode functions as the Ni barrier, whereby Ni can be effectively prevented from transitioning to the lowermost piezoelectric/electrostrictive portion with a lower Ni content from the piezoelectric/electrostrictive portion with a higher Ni content and forming a heterophase in the portion thereof.

[0054] Therefore, in the present invention, the electrode is preferably disposed in a state in which the electrode includes a region of the piezoelectric/electrostrictive portion which contributes to bending displacement or the like. For example, it is preferable that the electrodes 4, 5, and 6 be disposed in the region including near the center of 80 area % or more of the formation surface of the first piezoelectric/electrostrictive portion 12 and the second piezoelectric/electrostrictive portion 13 as shown in FIG. 1.

[0055] As shown in FIGS. 4(a) and 4(b), in the case where the common substrate 20 is used in common by a plurality of piezoelectric/electrostrictive devices 10 a to 10 c, the lowermost electrode 14 and the uppermost electrode 16 of the piezoelectric/electrostrictive devices 10 a, 10 b and 10 c may be used in common by the piezoelectric/electrostrictive devices 10 a to 10 c, and may be disposed as the integral electrode 14 in the region corresponding to piezoelectric/electrostrictive portions 2 a, 2 b and 2 c, and 3 a, 3 b and 3 c. Since such an integral electrode 14 need not have a shape corresponding to each of the piezoelectric/electrostrictive portions 2 a to 2 c and 3 a to 3 c, alignment is facilitated when forming the electrode.

[0056] In the present invention, as the material for the electrode, at least one metal selected from the group consisting of platinum, palladium, rhodium, gold, silver, and an alloy of these metals can be given. Of these, it is preferable to use platinum or an alloy containing platinum as a major component, since high heat resistance is secured during the heat treatment of the piezoelectric/electrostrictive portion. There are no specific limitations to the dimensions of the electrode. As shown in FIG. 6, the electrodes 4, 5, and 6 may have the same dimensions and be provided at the corresponding position in the same range in the direction of the thickness. As shown in FIG. 9, it is also preferable that the electrodes 4, 5, and 6 be formed in a larger range including the range corresponding to the electrode positioned in the lower layer in the order from the electrode 4. This configuration enables the piezoelectric/electrostrictive portion positioned in the upper layer to be distorted to a greater extent than the piezoelectric/electrostrictive portion positioned in the lower layer, whereby bending displacement can be caused to occur more effectively due to an increase in bending efficiency.

[0057] In the present invention, in the case of obtaining a large amount of bending displacement by increasing the drive voltage of the multilayered piezoelectric/electrostrictive device, the electrode 5 positioned in the middle layer is preferably formed in a range greater than the electrodes 4 and 6 positioned in the lower layer and the upper layer as shown in FIG. 10, or the electrode 5 positioned in the middle layer is preferably formed in a range smaller than the electrodes 4 and 6 positioned in the lower layer and the upper layer as shown in FIG. 11. This configuration prevents an electric field from being applied in the region near the end (in the lateral direction) in which the thickness of the piezoelectric/electrostrictive portions 2 and 3 tends to be decreased, whereby dielectric breakdown of the piezoelectric/electrostrictive portions 2 and 3 can be prevented. In the case where a difference in width is provided in the range in which the electrodes are formed, the difference in width is preferably optimized taking the electric field distribution into consideration. For example, the ratio of the electrode formation area (area of formation surface) of the electrodes 4 and 5 (or 5 and 6) adjacent with the piezoelectric/electrostrictive portion 2 (or 3) interposed therebetween is preferably 0.5-2, still more preferably 0.67-1.5, and particularly preferably 0.83-1.2. In FIGS. 9-11, a symbol P denotes the width of the lower electrode, a symbol Q denotes the width of the middle electrode, and a symbol R denotes the width of the upper electrode.

[0058] A method of manufacturing the multilayered piezoelectric/electrostrictive device of the present invention is described below. A piezoelectric/electrostrictive ceramic composition layer is formed on a ceramic substrate or an electrode formed on the surface of the substrate. As a method for forming the electrode, an ion beam method, sputtering method, vacuum deposition method, PVD method, ion plating method, CVD method, plating method, screen printing method, spraying method, and dipping method can be given. Of these, a sputtering method and a screen printing method are preferable from the viewpoint of bondability with the substrate and the piezoelectric/electrostrictive portion. The resulting electrode is integrated with the substrate and/or the piezoelectric/electrostrictive portion by a heat treatment at about 1000-1400° C. The heat treatment may be performed each time the electrode is formed, or may be performed together with a heat treatment performed for a piezoelectric/electrostrictive ceramic composition layer.

[0059] The piezoelectric/electrostrictive ceramic composition may be prepared by sintering and grinding a mixed raw material in which the raw materials are mixed corresponding to the composition, or by adding NiO to the presintered mixed raw material and further presintering and grinding the mixed raw material. A method for preparing a piezoelectric/electrostrictive ceramic composition which comprises a PbMg_(1/3)Nb_(2/3)O_(3—PbZrO) ₃—PbTiO₃three-component solid solution composition as an essential component is described below in detail as a representative example.

[0060] A single element such as Pb, Mg, Nb, Zr, or Ti, an oxide of each element (PbO, Pb₃O₄, MgO, Nb₂O₅, TiO₂, or ZrO₂, or the like), carbonate (MgCO₃ or the like), or a compound containing a plurality of these elements (MgNb₂O or the like) is mixed so that the content of each element becomes the composition ratio of a desired piezoelectric/electrostrictive ceramic composition to prepare a mixed raw material which is the essential component of the piezoelectric/electrostrictive ceramic composition.

[0061] The mixed raw material is presintered at 750-1300° C. After the addition of a desired amount of NiO, the mixture is mixed and sintered at 750-1300° C. to obtain a piezoelectric/electrostrictive ceramic composition. In the resulting piezoelectric/electrostrictive ceramic composition, the ratio of the diffraction intensity of the pyrochlore phase to the diffraction intensity of the perovskite phase measured by using an X-ray diffraction device is preferably 5% or less, and still more preferably 2% or less.

[0062] The resulting piezoelectric/electrostrictive ceramic composition is ground using a conventional grinding device such as a ball mill, attritor, or bead mill to obtain a powder with a desired particle size. The average particle size of the piezoelectric/electrostrictive ceramic composition obtained by grinding is preferably 0.1-1.0 μm, and still more preferably 0.3-0.7 μm. The particle size may be adjusted by subjecting the powder of the piezoelectric/electrostrictive ceramic composition obtained by grinding to a heat treatment at 400-750° C. In this case, finer particles are integrated with other particles to form a powder with a uniform particle size, whereby a piezoelectric/electrostrictive portion with a uniform particle size can be obtained. The piezoelectric/electrostrictive ceramic composition may be prepared by using an alkoxide method or a coprecipitation method, for example.

[0063] The piezoelectric/electrostrictive ceramic composition which comprises a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition as an essential component is obtained in the same manner as the piezoelectric/electrostrictive ceramic composition which comprises a PbMg_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition as an essential component except for presintering at once a mixed raw material prepared by mixing a single element such as Pb, Mg, Ni, Nb, Zr, or Ti, an oxide of each element (PbO, Pb3O₄, MgO, NiO, Nb₂O₅, TiO₂, ZrO₂, or the like), carbonate (MgCO₃ or the like), or a compound containing a plurality of each element (MgNb₂O or the like) so that the content of Pb, Mg, Ni, Nb, Zr, and Ti elements becomes the composition ratio of a desired piezoelectric/electrostrictive ceramic composition.

[0064] As a method for forming a piezoelectric/electrostrictive ceramic composition layer on the substrate, a screen printing method, spraying method, or dipping method can be given. Of these, it is preferable to use a screen printing method since layers can be continuously and easily formed in a highly accurate shape and thickness. An electrode is formed on the piezoelectric/electrostrictive ceramic composition layer formed on the surface of the substrate by using the above-described method. A piezoelectric/electrostrictive ceramic composition layer and an electrode are alternately and repeatedly formed on the electrode until a desired multilayered structure is obtained.

[0065] A layered product obtained by alternately layering the piezoelectric/electrostrictive ceramic composition layers and the electrodes on the surface of the substrate is integrally heated. This heat treatment causes the piezoelectric/electrostrictive portion formed of the piezoelectric/electrostrictive ceramic formed of the piezoelectric/electrostrictive ceramic composition to adhere to the substrate directly or through the electrode. The heat treatment is not necessarily performed integrally. The heat treatment may be performed each time the piezoelectric/electrostrictive ceramic composition layer is formed. However, it is preferable to integrally perform the heat treatment in a state in which the electrode is formed from the viewpoint of production efficiency.

[0066] The heat treatment temperature is preferably 1000-1400° C., and still more preferably 1100-1350° C. If the heat treatment temperature is less than 1000° C., the piezoelectric/electrostrictive portion may insufficiently adhere to the substrate or the electrode, or the density of the piezoelectric/electrostrictive portion may become inadequate. If the heat treatment temperature exceeds 1400° C., since the volatilization amount of Pb and Ni in the piezoelectric/electrostrictive ceramic composition is increased, it is difficult to form a piezoelectric/electrostrictive portion with a desired composition. The maximum temperature retention time during the heat treatment is preferably 10 minutes to 10 hours, and still more preferably 20 minutes to four hours. If the maximum temperature retention time is less than 10 minutes, densification of the piezoelectric/electrostrictive portion tends to be inadequate, whereby desired characteristics may not be obtained. If the maximum temperature retention time exceeds 10 hours, the total volatilization amount of Pb and Ni is increased even if the atmosphere is controlled, whereby the piezoelectric/electrostrictive characteristics may be decreased or dielectric breakdown is increased.

[0067] In order to form a piezoelectric/electrostrictive portion in a state in which the Ni content in the piezoelectric/electrostrictive ceramic composition is controlled in a desired amount, it is preferable to perform the heat treatment in the presence of an atmosphere control material having an Ni content approximately the same as the Ni content in the piezoelectric/electrostrictive ceramic composition. It is preferable that the atmosphere control material have a content of other materials approximately the same as that in the piezoelectric/electrostrictive ceramic composition in order to prevent volatilization of other components and securely obtain a piezoelectric/electrostrictive portion with a desired composition.

[0068] A polarization treatment is performed under suitable conditions. In this case, it is preferable to perform the polarization treatment by heating in the same manner as in a conventional method. The heating temperature is preferably 40-200° C., although the heating temperature varies depending on the Curie point of the piezoelectric/electrostrictive ceramic.

EXAMPLES

[0069] The present invention is described below in more detail by way of examples. However, the present invention is not limited to the following examples.

Examples 1-5 and Comparative Examples 1-4

[0070] A necessary number of a Pt electrode 4 (surface area of 0.4 mm×3 mm with thickness of 5 μm) was formed by using a screen printing method on a substrate 1 formed of ZrO₂ stabilized by Y₂O₃ having a shape as shown in FIGS. 5(a) to 5(c) (thin portion 1 c: 0.8×4 mm (dimensions)×100 μm (thickness)) which was formed by using a green sheet forming method and sintered. Each of the electrodes 4 was integrated with the substrate 1 (thin portion 1 c) by a heat treatment at 1300° C. for two hours.

[0071] By using a piezoelectric/electrostrictive ceramic composition having the compositional formula and the Ni content (mass %) shown in Table 1, the first piezoelectric/electrostrictive portion 12 having a surface area of 0.6 mm×2.8 mm with a thickness of 15 μm was formed on each of the electrode 4 having been integrated with the substrate 1 by using a screen printing method. Each of Pt electrodes 5 (surface area of 0.8 mm×4 mm with thickness of 5 μm) was formed on each of the resulting products by using a screen printing method. By using a piezoelectric/electrostrictive ceramic composition having the compositional formula and the Ni content (mass %) shown in Table 1, each of the second piezoelectric/electrostrictive portions 13 (surface area of 0.6 mm×2.8 mm with thickness of 15 μm) was formed on thus formed respective electrodes 5 by using a screen printing method. The “Ni content ratio (first/second)” shown in Table 1 is a value given by the ratio of the Ni content (mass %) in each piezoelectric/electrostrictive ceramic composition used for forming the first piezoelectric/electrostrictive portion 12 to the Ni content (mass %) in each piezoelectric/electrostrictive ceramic composition used for forming the second piezoelectric/electrostrictive portion 13.

[0072] Each of thus formed products was subjected to a heat treatment at 1275° C. for two hours in a container in the presence of an atmosphere control material having the same composition as the piezoelectric/electrostrictive ceramic composition used for forming the second piezoelectric/electrostrictive portion 13 in an NiO conversion amount of 0.002 mg/cm³ per unit volume of atmosphere. An Au electrode 6 (surface area of 0.4 mm×4 mm with thickness of 5 μm) was formed on thus treated product by using a screen printing method. Each of the resulting products was subjected to a heat treatment to obtain a multilayered piezoelectric/electrostrictive device (Examples 1-5 and Comparative Examples 1-4) as shown in FIGS. 5(a) to 5(c). TABLE 1 Piezoelectric/electrostrictive ceramic composition shown by Ni content Ni content ratio Compositional formula (mass %) (first/second) Comparative First piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 2.0 Example 1 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.935)Ni_(0.065))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.1 electrostrictive portion Comparative First piezoelectric Pb_(1.00) {(Mg_(0.967)Ni_(0.033))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.5 1.0 Example 2 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.967)Ni_(0.033))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.5 electrostrictive portion Example 1 First piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 0.3 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.543)Ni_(0.457))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.7 electrostrictive portion Example 2 First piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 0.2 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(1/3)Nb_(2/3))_(0.20)Ti_(0.43)Zr_(0.37)O₃ + NiO 1.0 electrostrictive portion Example 3 First piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 1.0 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 electrostrictive portion Example 4 First piezoelectric/ Pb_(1.00) {(Mg_(0.935)Ni_(0.065))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.1 0.5 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 electrostrictive portion Example 5 First piezoelectric/ Pb_(1.00) {(Mg_(0.478)Ni_(0.522))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.8 1.0 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.478)Ni_(0.522))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.8 electrostrictive portion Comparative First piezoelectric/ Pb_(1.00) {(Mg_(0.87)Ni_(0.13))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 0.2 0.1 Example 3 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(1/3)Nb_(2/3))_(0.20)Ti_(0.43)Zr_(0.37)O₃ + NiO 1.5 electrostrictive portion Comparative First piezoelectric/ Pb_(1.00) {(Mg_(0.347)Ni_(0.653))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 1.0 1.0 Example 4 electrostrictive portion Second piezoelectric/ Pb_(1.00) {(Mg_(0.347)Ni_(0.653))_(1/3)Nb_(2/3)}_(0.20)Ti_(0.43)Zr_(0.37)O₃ 1.0 electrostrictive portion

[0073] The thickness (μm) of each of the first piezoelectric/electrostrictive portions 12 and the second piezoelectric/electrostrictive portions 13 of each multilayered piezoelectric/electrostrictive devices, and the maximum particle size (μm) and the average particle size (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion were measured. The a ratio was calculated therefrom. The bending displacement (μm) of each multilayered piezoelectric/electrostrictive device was measured. The results are shown in Table 2. The measurement methods for the average particle size and the maximum particle size of the piezoelectric/electrostrictive ceramic, the thickness of the piezoelectric/electrostrictive portion, and the bending displacement are given below. (Average particle size and maximum particle size)

[0074] The average particle size and the maximum particle size of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion were measured by observing the cross section of the piezoelectric/electrostrictive portion in the layering direction using a scanning electron microscope. In more detail, a straight line was drawn on an arbitrary observed image (cross section of piezoelectric/electrostrictive portion), and the distance between the grain boundaries of each particle of the piezoelectric/electrostrictive ceramic which crossed the straight line was employed as the particle size of the particle. The particle sizes of 100 particles of the piezoelectric/electrostrictive ceramic were measured to calculate the average particle size and the maximum particle size. (Thickness of piezoelectric/electrostrictive portion)

[0075] The thickness of the piezoelectric/electrostrictive portion was measured by observing the cross section of the piezoelectric/electrostrictive portion in the layering direction using a scanning electron microscope. In more detail, the thickness of the piezoelectric/electrostrictive portion was measured at three points including the center and both ends of the cross section of the multilayered piezoelectric/electrostrictive device, and the average value of the thicknesses at the three points was employed as the thickness (μm) of the piezoelectric/electrostrictive portion. The ends of the cross section of the multilayered piezoelectric/electrostrictive device are ends of a portion which substantially exhibits characteristics of each piezoelectric/electrostrictive portion held between the electrodes. Specifically, the right end in FIG. 5(b) is a portion near the end of the middle electrode 5, and the left end is a portion near the ends of the upper electrode 6 and the lower electrode 4.

[0076] (Bending Displacement)

[0077] The bending displacement (μm) was measured using a laser displacement measurement device with applying voltage between the upper and lower electrodes so that an electric field of 50 V/mm occurs. In Table 2, the “average” of the bending displacement (μm) is the average value in the case of manufacturing the multilayered piezoelectric/electrostrictive devices of the examples and the comparative examples, ten pieces each, and measuring the bending displacement at the end (actuator portion 30 (see FIG. 5(b))). The “variation” is the difference between the maximum value and the minimum value of the measured bending displacement. TABLE 2 Piezoelectric/ electrostrictive ceramic Thickness of Maximum Average piezoelectric/ Bending displacement particle particle Electrostrictive (μm) size (μm) size (μm) portion (μm) Ratio a Average Variation Comparative First piezoelectric/ 1.5 0.2 11.2 0.01 2.92 0.30 Example 1 electrostrictive portion Second piezoelectric/ 1.6 0.2 11.4 0.02 electrostrictive portion Comparative First piezoelectric/ 0.9 0.15 10.5 0.01 2.00 0.25 Example 2 electrostrictive portion Second piezoelectric/ 0.8 0.13 10.8 0.01 electrostrictive portion Example 1 First piezoelectric/ 6.8 4.2 10.5 0.40 3.50 0.70 electrostrictive portion Second piezoelectric/ 7.0 4.2 10.8 0.39 electrostrictive portion Example 2 First piezoelectric/ 5.6 3.2 10.3 0.31 3.65 1.02 electrostrictive portion Second piezoelectric/ 5.8 3.1 10.1 0.31 electrostrictive portion Example 3 First piezoelectric/ 4.1 2.0 9.9 0.20 3.92 0.39 electrostrictive portion Second piezoelectric/ 4.2 2.1 10.1 0.21 electrostrictive portion Example 4 First piezoelectric/ 2.0 0.3 9.4 0.03 3.12 0.35 electrostrictive portion Second piezoelectric/ 2.4 0.4 10.3 0.04 electrostrictive portion Example 5 First piezoelectric/ 9.5 6.4 11.4 0.56 3.75 1.20 electrostrictive portion Second piezoelectric/ 8.8 5.7 10.9 0.52 electrostrictive portion Comparative First piezoelectric/ 10.3 6.4 10.0 0.64 3.82 1.72 Example 3 electrostrictive portion Second piezoelectric/ 10.1 6.5 9.8 0.66 electrostrictive portion Comparative First piezoelectric/ 10.8 7.4 10.5 0.70 3.85 1.85 Example 4 electrostrictive portion Second piezoelectric/ 10.2 6.7 9.9 0.68 electrostrictive portion

[0078] As is clear from the results shown in Table 2, it was found that the multilayered piezoelectric/electrostrictive devices of Examples 1-5 exhibit sufficient bending displacement in comparison with the multilayered piezoelectric/electrostrictive devices of Comparative Examples 1-4, and show small variation in bending displacement. This is considered to be because the a ratio of every piezoelectric/electrostrictive portion constituting each of the multilayered piezoelectric/electrostrictive devices is within the predetermined range in case of the multilayered piezoelectric/electrostrictive devices in Examples 1-5.

[0079] As described above, since the ratio of the average particle size of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion to the thickness of the piezoelectric/electrostrictive portion satisfies the predetermined relationship in each piezoelectric/electrostrictive portion, the multilayered piezoelectric/electrostrictive device of the present invention includes the piezoelectric/electrostrictive portion having extremely excellent piezoelectric/electrostrictive characteristics. This device is also excellent in vibration transfer characteristics between the substrate and the piezoelectric/electrostrictive portion, shows small variation in piezoelectric/electrostrictive characteristics among the piezoelectric/electrostrictive portions multilayered or even within the portions of a single piezoelectric/electrostrictive portion, and exhibits excellent durability. The multilayered piezoelectric/electrostrictive device of the present invention is suitable as a piezoelectric/electrostrictive device usable for forming a transmitter, sensor, actuator, or the like by making use of these characteristics. 

What is claimed is:
 1. A multilayered piezoelectric/electrostrictive device comprising a ceramic substrate, a plurality of piezoelectric/electrostrictive portions including a piezoelectric/electrostrictive ceramic formed of a piezoelectric/electrostrictive ceramic composition, and a plurality of electrodes electrically connected with the piezoelectric/electrostrictive portion, the piezoelectric/electrostrictive portions and the electrodes being alternately layered on the substrate, and a lowermost piezoelectric/electrostrictive portion of the piezoelectric/electrostrictive portions positioned in a lowermost layer adhering to the substrate directly or through a lowermost electrode of the electrodes positioned in a lowermost layer, wherein a ratio (α=A/B) of an average particle size (A) (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion to a thickness (B) (μm) of the piezoelectric/electrostrictive portion satisfies a relationship expressed by “0.02≦α≦0.6” in each of the piezoelectric/electrostrictive portions.
 2. The multilayered piezoelectric/electrostrictive device according to claim 1, wherein a maximum particle size (μm) of the piezoelectric/electrostrictive ceramic used for forming the piezoelectric/electrostrictive portion is smaller than the thickness (μm) of the piezoelectric/electrostrictive portion in each of the piezoelectric/electrostrictive portions.
 3. The multilayered piezoelectric/electrostrictive device according to claim 1, wherein an Ni content (NiO conversion) in the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion is 0.06-0.84 mass %, and wherein an Ni content (NiO conversion) in the piezoelectric/electrostrictive ceramic composition used for forming each of the piezoelectric/electrostrictive portions positioned in a layer above the lowermost piezoelectric/electrostrictive portion is equal to or greater than the Ni content (NiO conversion) in the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion.
 4. The multilayered piezoelectric/electrostrictive device according to claim 1, wherein the thickness of the piezoelectric/electrostrictive portion is 1-50 μm.
 5. The multilayered piezoelectric/electrostrictive device according to claim 1, wherein the piezoelectric/electrostrictive ceramic composition comprises a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition shown by the following formula (1) as an essential component: Pb_(x){(Mg_(1−y)Ni_(y))_((1/3)xa)Nb_(2/3)}_(b)Ti_(c)Zr_(d)O₃  (1) wherein 0.95≦x≦1.05, 0.05≦y≦0.50, 0.90≦a≦1.10, and each of b, c, and d is a decimal within a range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (b+c+d) is 1.000.
 6. The multilayered piezoelectric/electrostrictive device according to claim 1, wherein the piezoelectric/electrostrictive ceramic composition used for forming the lowermost piezoelectric/electrostrictive portion comprises a Pb(Mg,Ni)_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO₃ three-component solid solution composition shown by the following formula (2) as an essential component, and wherein the piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion positioned in a layer above the lowermost piezoelectric/electrostrictive portion comprises a PbMg_(1/3)Nb_(2/3)O₃—PbZrO₃—PbTiO three-component solid solution composition shown by the following formula (3) as an essential component and includes NiO: Pb_(x){(Mg_(1−y)Ni_(y))_((1/3)xa)Nb_(2/3)}_(b)Ti_(c)Zr_(d)O₃  (2) wherein 0.95≦x≦1.05, 0.05≦y≦0.50, 0.90≦a≦1.10, and each of b, c, and d is a decimal within a range enclosed by coordinates in which b, c, and d are axes of coordinates, (b, c, d)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (b+c+d) is 1.000; and Pb_(x)(Mg_(y/3)Nb_(2/3))_(a)Ti_(b)Zr_(c)O₃  (3) wherein 0.95≦x≦1.05, 0.95≦y≦1.050, and each of a, b, and c is a decimal in a range enclosed by coordinates in which b, c, and d are axes of coordinates, (a, b, c)=(0.550, 0.425, 0.025), (0.550, 0.325, 0.125), (0.375, 0.325, 0.300), (0.100, 0.425, 0.475), (0.100, 0.475, 0.425), and (0.375, 0.425, 0.200), provided that (a+b+c) is 1.000. 